The present invention relates to cameras with a photometric function and, in particular, to a camera with a photometric function having a function of displaying auxiliary information such as a focusing state and/or a focusing position in a superimposed manner on a subject image on a finder, and to an optical element for use in the camera.
Currently, many cameras have automatic focusing (AF) and automatic exposure (AE) functions, and it is necessary to present various information related to these functions to photographers. In addition, other various information such as the maximum number of shots, remaining battery power, and operating state of the flash should be presented to photographers. In the case of cameras including a finder, the information is commonly displayed in a superimposed manner on a subject image on the finder. Photographers may look into the finder to acquire the subject image (primary information necessary for photographing) and the accompanying information (hereinafter referred to as auxiliary information) at the same time.
For example, Japanese Patent Laid-open Publication No. 2002-072331A discloses a technique for displaying information about a focus detection area in a superimposed manner on a subject image on the finder. Japanese Patent Laid-open Publication No. 2004-133346A also discloses a technique for displaying various auxiliary information in a superimposed manner on a subject image on the finder by forming a projection image of the auxiliary information on the focusing screen.
Cameras with an automatic exposure (AE) function require photometric means to determine correct exposure. There are a number of such photometric means having a function of measuring the intensity of subject light incident through a photo-taking lens and employing a mechanism, due to its structure, for extracting part of the subject light toward the finder as branched light and measuring the intensity of the branched light. However, in the case of displaying various auxiliary information in a superimposed manner on a subject image on the finder, light toward the finder results in containing not only subject light for essential intensity measurement but also light for displaying the auxiliary information. For example, in the case of cameras incorporating an LED to be turned on when a focusing state is achieved and having a function of guiding light from the LED toward the finder and confirming on the finder whether the LED is turned on or off, subject light could not be measured accurately with entrance of light from the LED into photometric means.
In order to solve such a problem, Japanese Patent Laid-open Publication No. 2004-133346A, for example, also discloses a technique for disabling AF and AE functions while auxiliary information is displayed on the finder. This kind of time sharing control can prevent light for displaying the auxiliary information from affecting the photometric function for AE. However, the function of displaying the auxiliary information on the finder and the photometric function for AE cannot be utilized simultaneously, which exhibits a negative impact in that various restrictions are imposed on usage pattern.